Soumyadipta Rakshit

Morphology control of nickel oxalate by soft chemistry and conversion to nickel oxide for application in photocatalysis

The present work provides an effective methodology for controlled room-temperature aqueous synthesis of nickel oxalate (NiOX) nanosheets and nanoflakes in the presence of anion rich self-assembled bilayers of catanionic surfactant comprising of anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB). Encouragingly alteration of the CTAB/SDS ratio played an extraordinary role to form nanoflakes and nanosheets of NiOX. Our synthetic approach is combined with calcination to produce antiferromagnetic spherical and hexagonal nickel oxide (NiO) nanoparticles (NPs) as the end product. Synthesized nanostructured NiOX and NiO were characterized by X-ray diffraction study (XRD), energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). TEM studies illustrated that spherical NiO NPs have an average size around 5–10 nm and that of hexagonal NiO NPs have average width of about 22–27 nm. Temperature and field dependent magnetic properties of spherical and hexagonal NiO nanomaterials (NMs) were measured by using a SQUID magnetometer which revealed canted antiferromagnetic and spin glass nature, respectively. In addition, we report photocatalytic activity of NiO NMs, investigated on the photodegradation of phenol under ambient conditions, and as expected, the NiO having largest surface area showed best catalytic efficiency. This biomimetic catanionic surfactant inspired approach which require only metal ions as reactants have a definite potential towards an alternative, simple way of synthesizing metal oxide NMs.

Probing the spectral response of a new class of bioactive pyrazoline derivative in homogeneous solvents and cyclodextrin nanocavities: a spectroscopic exploration appended by quantum chemical calculations and molecular docking analysis

Time-dependent density functional theory (TD-DFT) calculations and molecular docking analysis provide valuable insights, in addition to experimental evidence, on the newly synthesized pyrazoline derivative 5-(1′-(4-bromophenyl)-3a′,4′,5′,6′,6a′-hexahydrocyclopentapyrazoline)-3-methyl-1-phenyl-1H-pyrazole-4-carbonitrile (PZ) as a fluorescence recognition probe and its photophysical signature in homogeneous and heterogeneous cyclodextrin (CD) environments, in addition to its insertion mechanism inside CD. The spectral trends of PZ do not appear to originate only from changes to the solvent polarity, but also indicate hydrogen bonding interactions with a homogeneous medium. The encapsulation of PZ within supramolecular α-, β- and γ-CD hosts was investigated using fluorescence spectroscopic techniques. The results show the formation of both 1 : 1 and 1 : 2 PZ–CD inclusion complexes with β-CD and only a 1 : 1 complex with γ-CD. The measured lifetimes and steady state anisotropy values also show the same trend and reveal the mode of interaction of the probe with the CD moiety. Furthermore, molecular docking studies performed via molecular mechanics methods (MMC) indicate that the pyrazoline moiety of PZ is most likely oriented towards the dip inside the cyclodextrin cavity. Solvent-dependent spectral data using TD-DFT calculations on the optimized ground and excited state structures of PZ were found to correlate well with the experimental findings.

A colorimetric and turn-on fluorescent chemosensor for selective detection of Hg2+: theoretical studies and intracellular applications

A new colorimetric, “turn-on” fluorescent chemosensor (DEAS-BPH) was synthesized for selective and sensitive recognition of Hg2+ ions with no interference from environmentally relevant metal ions in a mixed organo-aqueous medium. It was found that the presence of mercury induced nearly 27-fold fluorescence enhancement. This was attributed to the 1 : 2 metal–ligand complexation, ascertained by a Jobs plot, NMR titration and HRMS studies. A theoretical study was conducted to rationalize the colorimetric sensing behaviour of the probe on the basis of an intramolecular charge transfer (ICT) mechanism. In addition, morphological alteration upon complexation with mercury was explored with the aid of Field Emission Scanning Electron Microscope (FESEM) measurement. Results of MTT assay and fluorescence microscopic studies unveiled that the probe is cell permeable with low cytotoxicity. Furthermore, the reversibility of the sensor and its efficacy to function in a wide range of pH values designated the suitability to image intracellular Hg2+ ions in living HepG2 and Escherichia coli bacterial cells.

Controlled synthesis of spin glass nickel oxide nanoparticles and evaluation of their potential antimicrobial activity: A cost effective and eco friendly approach

Development of an easy sustainable synthetic pathway towards oxide nanomaterials (NMs) is a necessary challenge for nanotechnology research workers. Additionally, antimicrobial activity of oxide nanoparticles against multi drug resistance pathogenic bacteria motivates scientists to focus their research on oxide materials. We report here a cost effective, simple and eco-friendly pathway of synthesizing NiO nanoparticles (NPs). X-ray diffraction and energy dispersive X-ray study confirmed their crystallinity and composition. Field emission scanning electron microscope (FESEM) was employed to understand their surface architecture and the dimension of synthesized NiO NPs were found to be 20–30 nm from transmission electron microscope (TEM) study. The as synthesized NiO demonstrated typical spin glass behaviour which is one advantage of our synthetic procedure. Antimicrobial properties of NiO NPs were investigated using Gram negative and Gram positive bacteria and their bactericidal effects were determined from minimum inhibitory concentrations (MIC) and Minimum bactericidal concentrations (MBC). Haemolytic activity revealed the nontoxic nature of the NPs towards the blood proteins at MBC. TEM images of bacteria cells treated with NiO NPs showed irreversible damages to the cell wall leading to cell death. In light of our findings a possible mechanism of the antimicrobial effect of NiO NPs has been proposed.

Understanding the effect of size and shape of gold nanomaterials on nanometal surface energy transfer

Gold Nanomaterials (GNMs) interact with fluorophores via electromagnetic coupling under excitation. In this particular work we carried out (to the best of our knowledge for the first time) a comprehensive study of systematic quenching of a blue emitter 2-Anthracene Sulfonate (2-AS) in the presence of gold nanoparticles of different size and shape. We synthesized gold nanomaterials of four different dimensions [nanoparticle (0D), nanorod (1D), nanotriangle (2D) and nanobipyramids (3D)] and realized the underlying effect on the emitting dipole in terms of steady and time resolved fluorescence. Nanometal Surface Energy Transfer (NSET) has already been proved to be the best long range spectroscopic ruler so far. Many attempts have been made to understand the interaction between a fluorescent molecule and gold nanomaterials. But not a single model can interpret alone the interaction phenomena. We have opted three different models to compare the experimental and theoretical data. Due to the presence of size dependent absorptivity and dielectric function, modified CPS-Kuhn model was proved to be the worthiest to comprehend variance of behavior of an emitting dipole in close proximity to nanometal surface by coupling with the image dipole of gold nanomaterials.

Micellar charge induced emissive response of a bio-active 3-pyrazolyl-2-pyrazoline derivative: a spectroscopic and quantum chemical analysis

The medium charge specific excited state behaviour of a bio-active and fluorescent 3-pyrazolyl-2-pyrazoline derivative (PYZ) was systematically monitored in aqueous solutions of ionic (CTAB, SDS) and non-ionic (Triton X-100) micelles, applying steady state and time resolved fluorescence spectroscopy in addition to theoretical molecular simulations. PYZ displays complementary emission characteristics according to the nature of the effective charge of the micelles which was rationalized on the very fundamental basis of the frontier molecular orbital approach as obtained from quantum chemical calculations involving Time Dependent Density Functional Theory (TD-DFT) in combination with B3LYP exchange correlation function using 6-31G(d,p) as the basis set. Dynamic Light Scattering (DLS) measurements provided crucial information regarding the fluorescence quenching pattern of micelle bound PYZ by quencher CpCl. This study essentially accentuates PYZs photophysical response in different micellar media in conjunction with their individual mode of electrostatic interaction therein. The theoretically calculated HOMO–LUMO energy gap values provide adequate information about the emissive behaviour of PYZ in ionic micellar media. The variation in the lifetime values of PYZ in aqueous and micellar media act as added evidence of the fact that PYZ basically resides in different micro-environments as introduced by the respective micelles. Conclusively it was observed that, in the excited state, PYZ responded promptly and uniquely according to the nature of the micellar charge.

Toxicological assessment of PEG functionalized f-block rare earth phosphate nanorods

The emerging development of rare earth nanotechnology in daily science has aroused serious concerns regarding its impact on health care systems. Despite the potential uses of rare earth (RE) nanoparticles for targeted drug delivery, detection/diagnosis and imaging, potential nanoparticle toxicity must be investigated before any in vivo medicinal applications can move forward. In this account, we illustrate the toxicological assessment of polyethylene glycol (PEG) functionalised Ln3+ (Ce3+, Tb3+) doped rare earth phosphate (LaPO4) nanorods. The first part of the work describes the synthesis of the nanorods employing a biologically compatible reaction environment using a H2O–EtOH solvent mixture, reflux temperature and a ligand exchange methodology. Thereafter, the synthesized materials have been purified and characterized. The later part of the work discusses the in vivo toxicity of the nanomaterial. Synthesized nanorods were suspended in a buffer and administered to mice through intraperitoneal (IP) injection over a period of 7 days (high dose 125 mg kg−1) and 28 days (high dose 125 mg kg−1 and low dose 12.5 mg kg−1). Analysis of the serum biochemistry and haematology followed by histopathology indicates inflammation in the liver. The biodistributions of rare earth ions (La3+, Ce3+ and Tb3+) were analyzed using inductively coupled plasma mass spectrometry (ICPMS). Additionally, cellular viability of the synthesized nanorods was also studied using spleen mononuclear cells of Swiss albino mice.

Deciphering the Role of the Length of the Corona in Controlled NSET within Triblock Copolymers.

Nanometal surface energy transfer (NSET) from 2-anthracene sulfonate (2-AS) to gold nanoparticles in water-soluble triblock copolymers (TBP) P123 (PEO19PPO69PEO19) and F127 (PEO100PPO65PEO100) is systematically investigated. Fluorescence lifetime and anisotropy experiments provide thorough information on the locations of the 2-AS within these micelles. Variation in the size of the micellar corona region of the TBP is found to be the prime factor for different positions of 2-AS in them. Of late, nanometal surface energy transfer (NSET) from the donor probe to the surface of the metal nanoparticles has emerged as a potential tool for sensing and biolabeling. In the present work, the quenching of emission of the water-soluble 2-AS confined in the two different triblock copolymers in the proximity of a monolayer of the gold nanoparticles has been explored. Closer agreement between the experimental and theoretical characteristic distances has been found across the full wavelength range by the NSET approach. Understanding the location of the water-soluble dye in the vicinity of a polymeric drug delivery system is of significant importance, and how altered locations can trigger different controlled energy transfer efficiency from the 2-AS to the surfaces of gold nanoparticles (GNPs) has been discussed. This strategy could offer a new prospect in designing novel optical materials for chemical sensing and light harvesting endeavors.

Spectroscopic and Quantum Mechanical Approach of Solvatochromic Immobilization: Modulation of Electronic Structure and Excited-State Properties of 1,8-Naphthalimide Derivative

AbstractPhotophysical and spectroscopic properties of a fluorescent analogue, 2-(5-selenocyanato-pentyl)-6-chlorobenzo- [de]isoquinoline-1,3-dione (NP) in different solvents has been described in this paper using steady-state, time resolved spectroscopy and density functional theory (DFT) calculation. Stoke’s shifted emission band in different solvents clearly demonstrate the highly polar character of the excited state, which is also supported by the enhancement of dipole moment of the molecule upon photoexcitation. Spectroscopic studies and multiple linear regression analysis method reveal that the solvatochromic behavior of the probe depends not only on the polarity of the medium but also on the hydrogen bonding interaction with the solvents. When the solvent effect was taken into account, the computed results show encouraging agreement with known experimental data. This article reveals the excellent correlation between the predicted and experimental spectral data of 1,8-naphthalimide derivative, providing a useful tool in the design of new fluorogenic probes having potential therapeutic activity. Graphical AbstractSolvent dependent spectroscopic measurements of 1,8 Naphthalimide in corroboration with quantum chemical calculation.

Polymer-fabricated synthesis of cerium oxide nanoparticles and applications as a green catalyst towards multicomponent transformation with size-dependent activity studies

The present study primarily emphasizes the polymer-directed synthesis of cerium oxide nanoparticles (CeONP). Prior to the synthesis of CeONP, nanoflakes of the precursor cerium oxalate (CeOX) were first prepared by employing an AOT/lecithin/iso-octane/H2O mixed reverse microemulsion system and a polymer was added to the reaction medium to accomplish a dual purpose as both an additive and a structure-directing agent. Three polymers, namely, P123 (triblock copolymer), 17R4 (reverse triblock copolymer) and polyvinylpyrrolidone (PVP), were used as additives. Interestingly, the use of various polymers caused the synthesis of spherical cerium oxide nanoparticles within different size ranges (≈28.56 nm, 24.33 nm and 14.28 nm). Characterization of the synthesized CeONP was conducted by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD) and Raman spectroscopy. The latter part of the study investigated their size-dependent catalytic activity in three-component reactions between nitrostyrene, 1,3-dicarbonyl compound, and aromatic primary amines to produce N-arylpyrrole as the desired product. The surface area of nanoceria (CeO2) was determined by BET measurements. Variations in size were found to directly affect the yield of the reactions. TEM analysis both before and after catalysis indicated the participation of the edges of the particles in the reaction.